The MP4000 series rig is a purpose designed rig able to construct large diameter piles in very low headroom conditions by the operation of the “Martello” technique whereby the auger, or digging tool (which is not fixed to the base of the kelly bar, but has a hollow stem) is able to slide up and down a sectionally extendable kelly bar to depths in excess of 40m in just 3.5m of headroom.